With finer and finer semiconductor devices coming into use, the accuracy requirement for etching of samples such as wafers has been becoming severer year by year. To enable micro-patterns on wafer surfaces to be processed with high accuracy by a plasma processing apparatus, controlling the wafer surface temperature during etching is important. With larger-area wafers and higher etching rates being in demand, however, the magnitude of high-frequency power applied to the plasma processing apparatus tends to grow larger. For etching of insulating films, in particular, large power on the order of kilowatts has come to be applied to the plasma processing apparatus. When a larger power is used to etch a wafer surface, the impact energy of ions striking the wafer surface increases. This has been causing a problem of excessive temperature rises in wafers being etched. With higher form accuracy also being requested of wafer etching, a means for quickly and accurately controlling the temperature of a wafer being processed is demanded.
In a plasma processing apparatus, the surface temperature of a wafer can be controlled by controlling the surface temperature of the sample stage (electrostatic adsorption electrode) that is in contact with the back surface of the wafer via a heat transfer medium. According to a prior-art technique, the surface temperature of the sample stage is controlled by flowing a liquid refrigerant through a refrigerant flow path formed inside the sample stage. The liquid refrigerant is supplied to the flow path in the sample stage after being adjusted to a target temperature by a cooling unit or a heating unit provided in a refrigerant supply system. Besides, such a refrigerant supply system is configured such that the liquid refrigerant is sent out after once being stored in a tank and the liquid refrigerant has a large heat capacity, so that the refrigerant supply system is effective in keeping the surface temperature of a wafer constant. Since the temperature response of such a refrigerant supply system is slow, however, the refrigerant supply system is not capable of quick temperature control and its heat exchange efficiency is low. Besides, plasma processing apparatuses have been growing in size to cope with high input heats used in recent years. It has therefore been difficult to optimally control the surface temperature of a wafer being etched.
Under the circumstances, a direct expansion refrigerant supply system (hereinafter referred to as “a direct expansion refrigerating system”) have been proposed, for example, in Japanese Patent Application Laid-Open Publication No. 2005-89864 and Japanese Patent Application Laid-Open Publication No. 2003-174016. In each of such direct expansion refrigerating systems, a refrigerant circulation system including a compressor for compressing refrigerant, a condenser for condensing the compressed refrigerant, and an expansion valve for expanding the refrigerant is provided for a sample stage and the sample stage is cooled by evaporating the refrigerant in a refrigerant flow path formed in the sample stage. Since a direct expansion refrigerating system makes use of the latent heat of refrigerant vaporization, its cooling efficiency is high and it can quickly control by pressure the refrigerant vaporization temperature. Hence, applying a direct expansion refrigerant supply system to a sample stage of a plasma processing apparatus makes it possible to efficiently and quickly control the temperature of a semiconductor wafer being etched using a high input heat.